The results of three-dimensional numerical simulations of the dynamic motion of single drops rising in viscoelastic Chilcott–Rallison (FENE-CR) model fluids are presented. The simulations are performed using a combination of a coupled level-set/volume-of-fluid (CLSVOF) method and a hydrodynamic scheme with formal second-order accuracy. In our study, we address the rising motion of a drop exhibiting a range of small to large deformations. It is shown that the dynamic motion of the drop largely depends on the FENE-CR model parameters: the extensibility parameter L and the Deborah number strongly influence the viscoelastic characteristics of the drop. It is numerically shown that these parameters determine the characteristic cusp formation at the tail of the drop, similar to the case of bubble motion. We also discuss the difference between drop motion and bubble motion in viscoelastic FENE-CR model fluids.
In this work, the effect of alcohol addition on the liquid-phase volumetric mass transfer coefficient, kLaR, is studied in an external-loop airlift reactor with a porous plate using an air–water system to which methanol, ethanol or propanol was added in concentrations ranging from 0.002 to 1 wt%. The experimental results show that the addition of small amounts of alcohol increases dramatically the liquid-phase volumetric mass transfer coefficient in the riser, due to smaller bubble diameter than with the water system. This behavior is enhanced by alcohols with long carbon chain lengths, which may be probably explained on the basis of the inhibition of bubble-bubble coalescence at the gas sparger plate and in the liquid. This surprising result can be explained by a strong increase in kL values in liquid-phase volumetric mass transfer coefficients due to the increasing amount of small bubbles leading to larger partial pressure of transfer component within bubbles based on capillary pressure. A remarkable effect of alcohol addition on liquid-phase volumetric mass transfer coefficient was not observed above the critical concentration of each alcohol.
The purpose of the present study is to develop a new nanoparticle-classification technique to replace centrifugal separation method. To identify size-dependent particle properties, we investigated the dispersion, classification, and surface potential of silica particles treated with a bead mill, which was used to create a nanoparticle dispersion. The zeta potential of the particles in the dispersed slurry exhibited clear size dependence at tm = 30 min. That is, the zeta potential of the smaller particles was more negative than that of larger particles. Hence, the particles were classified using an EFFF system, in which the bottom and top plates of the channel served as negative and positive electrodes, respectively. Using a low applied potential, the 50% separation cut-size was 45 nm. This method prevented deposition of negatively charged silica particles on the bottom plate and allowed continuous operation. Results of theoretical calculations supported qualitatively the experimental results obtained in this study.
Differential scanning calorimetric analysis was employed to determine the thermal property of the inclusion compounds; the purpose of performing the analysis was to elucidate the possibility of its use as a tool for predicting host selectivity to a given isomer mixture. From the analysis, it was observed that the energy of guanidinium 4,4′-biphenyldisulfonate (G2BPDS·(p-xylene)) is the highest among all inclusion compounds, whereas that of G2BPDS·(m-xylene) is the lowest among them. The result agrees with the selective preference of the G2BPDS host in a previous experiment. Similarly, the guest release onset temperature of the G2BPDS inclusion compounds also decreased in the order G2BPDS·(p-xylene) > G2BPDS·(o-xylene) > G2BPDS·(m-xylene). In the case of guanidinium 2,6-naphthalenedisulfonate (G2NDS) inclusion compounds, both the energy and the guest release onset temperature of G2NDS·(p-xylene) were higher than those of G2NDS·3(o-xylene). In fact, the structure of G2NDS·(p-xylene) was stabilized to a great extent by the CH···O interaction between the host and guest as compared to the G2NDS·3(o-xylene) structure. Consequently, from the good agreement between the thermal property of inclusion compounds and host selectivity, it was noted that the differential scanning calorimetric study of inclusion compounds can be performed to predict the host selectivity prior to the competition experiment.
Defluidization and a decline in fluidization quality were observed in reactions involving a decrease in gas volume. This was due to a reduction in gas velocity in the emulsion phase owing to the reactions. The decrease in the gas velocity led to a reduction in the emulsion phase voidage. Finally, a part of the fluidized bed was defluidized and lifted up through the column like a moving piston. In the present study, methanation of carbon dioxide was carried out as a model reaction, and the effect of the two-stage distribution of the fluidizing gas on the improvement of the fluidization quality was investigated. The bed was fluidized by supplying hydrogen from the bottom of the fluidized bed. The other reactant, carbon dioxide, was supplied from the bottom distributor and a secondary gas inlet. By using this method, it was possible to avoid defluidization. The influences of the level of the secondary inlet and the distribution ratio of carbon dioxide on fluidization quality were studied by plotting two parameters that affect fluidization quality.
As a part of the development of process technology related to the manufacture of polylactic acid, it is important to obtain data on the correlation of the moisture content ratio and water vapor partial pressure with respect to lactic acid concentration. To eliminate the effects of the mixing of lactic acid with the water vapor, we have tested the combination of a water vapor transmitting filter and an Othmer equilibrium still, and determined the following. 1) For heating temperatures of 135°C and 150°C, the moisture content ratio in the lactic acid is reduced to 2% or less in two hours. After that, however, the decrease becomes gradual, so it is reasonable to consider that as the stopping point. 2) The reason for the first result is that, for these heating temperatures, moisture evaporation maintains a constant partial pressure down to a moisture content of 2%, but the vapor pressure decreases after that point in accordance with Henry’s law.
In this study, domestic and international chemical accident databases are analyzed, and a chemical accident reporting system is developed using chemical accident classification codes. These codes are revised by adopting the data collected in 2115 cases of chemical accidents that occurred in S. Korea over the last 20 years. The revised classification codes are composed of 12 upper, 64 middle, and 276 lower classes. The developed database is composed of data input, data list, and data search modules as well as statistic and analysis modules. Module operations help obtain information on relationships between accident data attributes that are not apparent, in addition to simple statistical results. The chemical accident tracking system is available on the Internet, and the data are treated using an on-line analytical system. The records are statistically analyzed to identify type of accidents that occurs frequently in Korean chemical companies, as well as the accident data and materials involved. We expect the results of this study to be useful in reporting for developing a management of system for prevention of chemical accidents, and improve the manageability of the designed system.
An effective method for the extraction of berberine (BER), palmatine (PAL), and jatrorrhizine (JAT) from Coscinium fenestratum by using microwave-assisted extraction (MAE) was developed in both an open (at atmospheric pressure) and closed vessel (under a pressurized condition). The extraction yields of BER yields obtained by using MAE under optimum conditions for 15 min (60% EtOH, material/solvent ratio 1.00 g:40 mL, microwave output power 300 W) in an open vessel at a boiling point of 83°C (25.20 mg/g) and in a closed vessel at 160°C (27.35 mg/g) were higher than those obtained using Soxhlet extraction for 8 h (24.37 mg/g) and extraction with 0.2% sulfuric acid for 24 h (21.82 mg/g). JAT (2.36 mg/g) and PAL (0.73 mg/g) extraction yields were observed to be the highest at 170°C for 15 min. Extraction using water as a solvent at 160°C for 15 min yielded the same level of BER amount (20.31 mg/g) as that obtained using 0.2% sulfuric acid for 24 h. This high extraction yield could be due to the alcohol-like characteristics of water at high temperature. BER degradation was observed at a temperature above 160°C. An additive such as EtOH or NaCl could reduce BER degradation. MAE is more effective than conventional extraction methods with regard to the extraction time and extraction yield for extracting protoberberine alkaloids from C. fenestratum.
Zeolite β was cost-effectively synthesized by the direct crystallization conversion of silicic and aluminium source powders using tetraethylammonium bromide (TEABr) as the structure-directing agent. The prepared samples were characterized by X-ray diffraction (XRD), temperature-programmed desorption of ammonium (NH3-TPD), Fourier-transform infrared spectroscopy (FT-IR), and N2 adsorption-desorption techniques. The characterization results indicated that the acidity and the pore structure of the synthesized zeolite were consistent with the standard zeolite β, although a trace of stray crystal of mordenite was observed. The lab-synthesized zeolite β, which was used as the additive in the USY-based fluid catalytic cracking (FCC) catalyst, exhibited a performance in catalytic cracking reaction of heavy oil feed that was similar to the performance of the standard zeolite β.
A tube radial distribution chromatography (TRDC) system has been developed using an open capillary tube and an aqueous–organic solvent mixture as a carrier solution under laminar flow conditions. In this study, we examine the elution behavior of carboxylated polymer particles (1.0 μm diameter) together with fluorescein isothiocyanate in the TRDC system in order to extend our knowledge regarding the separation performance of the system. The model analyte solution of fluorescein isothiocyanate and carboxylated polymer particles was injected into the open polyethylene capillary tube by the gravity method, and subsequently delivered through the capillary tube with the carrier solution of the water–acetonitrile–ethyl acetate mixture (15:3:2 volume ratio) using a microsyringe pump. On-capillary detection was performed for the analytes using an absorption detector, which indicated individual elution times and peak shapes on the chromatograms. We discuss the observed phenomena considering the separation mechanism of the TRDC system.
A model in which the reaction parameters of catalyst layers from microscopic to macroscopic scales are the main focus was systematically developed for polymer electrolyte fuel cells (PEFCs). The effect of oxygen-containing species adsorbed on the Pt surface at the microscopic three-phase boundary (Qox), which suppresses the oxygen reduction reaction (ORR), was taken into account in the PEFC model. Qox was expressed as a reaction parameter in terms of the coverage factor, and was included in the Tafel reaction equation. The advantages of our model were verified by carrying out the model validation, in which the results of cell performance obtained by simulation agreed very well with experimented results. Because of this key improvement, the developed model was more realistic and accurate. The simulation results also demonstrates that the effect of adsorbed oxygen-containing species is a very important reaction parameter that influences cell performance and must be considered in order to achieve high-performance PEFCs.
Catalytic activity of various solid acid catalysts is evaluated for the continuous hydroxyalkylation of p-cresol to [2,2′-methylenebis(4-methylphenol)] (DAM) in a fixed bed reactor. This is an industrially important process generally carried out in the presence of mineral acids. In the present study, we show that solid acids can be successfully used for this important process. The characterization of these solid acids is done using ammonia TPD measurement based on which the observed activity results can be explained. The performance of both batch and continuous operation has been studied for the hydroxyalkylation of p-cresol using the montmorillonite KSF/0 catalyst. The effect of reaction parameters such as mole ratio, temperature and catalyst concentration on the conversion of p-cresol and DAM selectivity have also been studied in both batch and fixed bed reactors. Significant difference is observed on the conversion of p-cresol and DAM selectivity with changing flow rate of reaction mixture in continuous operation.